object rest spread useBuiltIns option (babel#4491)

* feat(transform-object-rest-spread): add polyfill=false option to avoid extends helper

* object-rest-spread: add useBuiltIns option

* add test for invalid option

packages/babel-plugin-transform-object-rest-spread/README.md

@@ -2,6 +2,15 @@
 
 Compile object rest and spread to ES5
 
+```js
+// source
+z = { x, ...y };
+
+// compiled
+_extends = Object.assign || function(target) { ... }
+z = _extends({ x }, y);
+```
+
 ## Installation
 
 ```sh
@@ -20,6 +29,25 @@ $ npm install babel-plugin-transform-object-rest-spread
 }
 ```
 
+## Options
+
+This plugin will use babel's `extends` helper, which will polyfill `Object.assign` by default.
+
+* `useBuiltIns` - Do not use Babel's helper's and just transform to use the built-in method (Disabled by default).
+
+```js
+{
+  "plugins": [
+    ["transform-object-rest-spread", { "useBuiltIns": true }]
+  ]
+}
+
+// source
+z = { x, ...y };
+// compiled
+z = Object.assign({ x }, y);
+```
+
 ### Via CLI
 
 ```sh

packages/babel-plugin-transform-object-rest-spread/src/index.js

@@ -15,6 +15,11 @@ export default function ({ types: t }) {
       ObjectExpression(path, file) {
         if (!hasSpread(path.node)) return;
 
+        let useBuiltIns = file.opts.useBuiltIns || false;
+        if (typeof useBuiltIns !== "boolean") {
+          throw new Error("transform-object-rest-spread currently only accepts a boolean option for useBuiltIns (defaults to false)");
+        }
+
         let args = [];
         let props = [];
 
@@ -39,7 +44,11 @@ export default function ({ types: t }) {
           args.unshift(t.objectExpression([]));
         }
 
-        path.replaceWith(t.callExpression(file.addHelper("extends"), args));
+        const helper = useBuiltIns ?
+          t.memberExpression(t.identifier("Object"), t.identifier("assign")) :
+          file.addHelper("extends");
+
+        path.replaceWith(t.callExpression(helper, args));
       }
     }
   };

packages/babel-plugin-transform-object-rest-spread/test/fixtures/useBuiltIns/assignment-invalid-option/actual.js

@@ -0,0 +1 @@
+z = { x, ...y };

packages/babel-plugin-transform-object-rest-spread/test/fixtures/useBuiltIns/assignment-invalid-option/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": [["transform-object-rest-spread", { "useBuiltIns": "invalidOption" }]],
+  "throws": "transform-object-rest-spread currently only accepts a boolean option for useBuiltIns (defaults to false)"
+}

packages/babel-plugin-transform-object-rest-spread/test/fixtures/useBuiltIns/assignment-true/actual.js

@@ -0,0 +1 @@
+z = { x, ...y };

packages/babel-plugin-transform-object-rest-spread/test/fixtures/useBuiltIns/assignment-true/expected.js

@@ -0,0 +1 @@
+z = Object.assign({ x }, y);

packages/babel-plugin-transform-object-rest-spread/test/fixtures/useBuiltIns/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": [["transform-object-rest-spread", { "useBuiltIns": true }]]
+}